Inkjet printing is a non-impact printing method that, in response to a digital signal, produces droplets of ink that are deposited on a recording element. Today, inkjet printing systems are used in a variety of capacities in industrial, home, and office environments. The quality of inkjet prints continues to improve, however, inkjet prints are disadvantaged because they lack durability, often being less stable relative to environmental factors (light, ozone, etc.) and more sensitive to water and abrasion.
One way of overcoming these disadvantages is to laminate or encapsulated inkjet prints. When an inkjet print is laminated, a transparent overlay is adhered to the inkjet print. Typically, this is accomplished using an adhesive activated by heat, pressure, or both. The transparent overlay physically protects the print and seals it from ingress of water. When an inkjet print is encapsulated, the print is positioned between two laminating sheets, at least one of which is transparent. Then some combination of the print and the laminating sheets are adhered usually using an adhesive activated by heat, pressure, or both. Typically, encapsulation is most effective when the laminating sheets extend beyond the print and are bonded to each other at the extremities, thus preventing ingress of water through exposed edges of the print.
Lamination and encapsulation both have disadvantages in that they are expensive processes requiring additional materials and handling by the user. Moreover, inkjet inks remained trapped within the recording element which can degrade image quality by causing stain or migration of the print on storage or exposure. Laminate materials and adhesives can often deteriorate over time causing surface defects including, for example, cracking. Laminates do not always adhere well to inkjet prints. The quality and uniformity of adhesion can depend on the material nature of the recording element, the type of ink, and the volume of ink printed per unit area of recording element (ink laydown). The latter is particularly significant when the inkjet print has photographic image quality because heavy laydowns of ink are necessary to achieve the necessary superb image quality.
As an alternative to lamination or encapsulation, inkjet recording elements having a nascent protective layer coated on a support are known. The nascent protective layer is really a special chemical layer designed such that during the inkjet printing process, the inks penetrate the layer, and after printing is complete, the layer is fused using heat and/or pressure so that it seals and protects the print. This process is often referred to as the incorporated approach because the nascent protective material is incorporated into the recording element during its production.
However, the incorporated approach is limited because it is difficult to obtain a final protected print that is uniform in gloss and clarity and free of surface defects such as blistering and cracking. Limitations are especially apparent when the final protected print must have superb image quality, e.g., when it is for photographic or medical diagnostic applications. A recording element for these applications may have one or more of these layers underlying the nascent protective layer to help manage a heavy laydown of ink. After printing, the bulk of the ink, commonly referred to as the carrier, is retained somewhere in the dual layer system. If too much carrier resides in the nascent protective layer during fusing, it will not fuse properly and any of the aforementioned undesirable effects may be observed.
This condition worsens when the carrier resides predominately in an ink-receiving layer during and/or after fusing of the nascent protective layer, and then migrates within the ink-receiving layer, or from the ink-receiving layer and into the fused protective layer. Migration of the carrier within the ink-receiving layer causes deterioration of image quality, e.g., loss of image sharpness and blotchiness, and migration into the fused protective layer causes any of the aforementioned undesirable effects.
Examples of inkjet printing methods that employs the incorporated approach are described in U.S. Pat. No. 6,114,020, issued to Misuda et al., on Sep. 5, 2000; U.S. Pat. No. 4,832,984, issued to Hasegawa et al., on May 23, 1989; and U.S. Pat. No. 4,785,313, issued to Higuma et al., on Nov. 15, 1988.
European Patent Application 1 284 186 A2 describes a fixing apparatus and an image fixing method for improving the gloss of an inkjet image recorded on an inkjet recording material. The inkjet recording material includes a porous top layer which can be thermally fixed. After the image has been printed, the recording material is held in “a suspended state” before it is passed between a pair of fixing belts or rollers that are held at some elevated temperature and pressure.
Japanese Unexamined Patent Publication 2002-283553 A describes an inkjet recording device for controlling the gloss and clarity of an image surface of a recording medium. The device includes inkjet printing means for generating a printed image on a recording medium and fixing means for heating and pressing the printed image. The recording medium has a thermoplastic resin layer that receives ink and is subsequently fixed.
U.S. Pat. No. 6,394,669 B1, issued to Janosky et al., on May 28, 2002, discloses a post-print treatment processor for a photofinishing apparatus. Printed media is transported to a post-treatment processor. The post-treatment processor stations dry the media and apply a durable material on the printed media. In preferred embodiments, drying is accomplished using infrared radiation technology and application of the durable material is accomplished by laminating a clear protective film to the imaged side of the printed media.
U.S. Patent Application Publication 2002/0027587 A1 describes an apparatus and method for forming prints. A recording medium having thermoplastic resin particles on a surface layer is printed. Subsequently the resin particles are made transparent by a heating and pressing device. U.S. Patent Application Publication 2002/0008747 A1 describes a similar method.
U.S. Pat. No. 6,357,871 B1 describes an inkjet recording medium and apparatus for preparing an inkjet printed product. The inkjet recording medium has a layer of fine particles of a thermoplastic organic polymer that are dissolved or melted after inkjet recording to form a layer wherein the particles are fused to one another. Fusing the particles involves a step of heating the layer followed by an impressing step of passing the recording medium between a pair of press rolls while the layer is still in a plastic state after the heating step.
All of the aforementioned art are disadvantaged in that the bulk of the ink, or carrier, is trapped within the recording element after the protective layer is formed which leads to the problems described above.
U.S. Pat. No. 6,332,679 B1 describes an inkjet printer used to form an image on a recording medium. The recording medium includes a porous surface layer that is flattened by simultaneously pressing and heating the layer to form a flattened layer. Pressing is carried out by passing the imaged recording medium through a nip created by a pair of rollers. The nip is defined as a nip region having a point A at which the ink solvent contained in the recording medium reaches the boiling point, and a point B at which the porous layer of the recording medium loses its liquid permeation property.
The disadvantage associated with this method and apparatus is that ink solvent removal and flattening of the layer are carried out in the same step with very little physical distance between point A and point B. Therefore, neither step can be individually optimized and/or controlled. As a result, the flexibility of the method and apparatus to accommodate a broad range of recording media and ink volume laydowns is limited to those combinations that meet the temperature, pressure and transport speed conditions of the nip region. Another problem with this method and apparatus is that in order to remove enough ink solvent the temperature of the flattening roller must be high enough in order to cause sufficient evaporation before the liquid permeation property is eliminated. If the temperature is too high, the support can deform and release of the recording medium from the flattening roller becomes problematic. Additionally, the evaporated ink solvent can condense on the flattening roller making it difficult to maintain the temperature of the flattening roller. The condensed solvent can also redeposit on the surface or the recording medium increasing the potential for image defects.
U.S. Pat. No. 6,120,199 describes an inkjet printing apparatus having a heating fixation unit and a fixing unit. The heating fixation unit includes a fan that blows heated air over the surface of an imaged recording medium in an attempt to dry the surface before it enters the fixing unit. While ink solvent is allowed to escape from the imaged recording medium, the amount of ink solvent removed cannot be adequately controlled. Therefore, the reliability of the apparatus is reduced.
Additionally, the reliability of the apparatus also depends on a clean separation of the imaged recording medium from the fixing unit in processes that involve portions of the fixing unit providing pressure and energy by directly contacting the imaged recording medium. Prior to this step of the process, a portion of the imaged recording medium is tackified by heat (heated air, for example) to form a continuous protective overcoat over the imaged recording medium. However, in the event, any portion of the tackified imaged recording medium sticks to a portion of the fixing unit, overall image quality can be reduced or cause the apparatus to jam and may even damage the fixing unit.
Several methods have been developed in order to increase the likelihood of the imaged recording medium cleanly separating from the fixing unit, especially for fixing units that incorporate rollers. For example, it is known to use a thin coating of release agents on the rollers of the fixing unit. U.S. Pat. No. 5,824,416 discloses using different types coating materials on a fixing unit. Alternatively, a releasing agent can be used in the recording medium, preferably in the outermost layer of the recording medium. Examples of such releasing agents include: waxes, such as carnauba wax, paraffin wax, micro crystalline wax and castor wax; higher fatty acids or derivatives thereof like metal salts and esters; polyamide-based resins, petroleum-based resins, rosin derivatives, coumarone-indene resins, terpene-based resins, novolak-based resins, styrene-based resins, and olefin-based resins such as polyethylene, polypropylene, polybutene, oxidated polyolefins and vinyl ether-based resins.
The overall image quality of the converted recording element is also dependent on the smoothness of the surface. One commonly used measurement to quantify the converted surface is the specular gloss that associated with the capability of a surface to reflect light in a prescribed angle. This method of measurement is described in ASTM-D523.